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J1me 1966 F. J. LA RUSSA ETAL MICROWAVE PHASE SHIFTER Filed March 26,1962 5 Sheets-Sheet 1 -16 FIG. 2

SHORT CIRCUIT- f .5. 132 1 [SHORT CIRCUIT 1 r34 28 3o b .v x x HINVENTORS T FRANCIS J. LuRUSSA BY ERNEST J. WILKINSON ATTORNEY June 1966F. J. LA RUSSA ETAL 3,258,721

MICROWAVE PHASE SHIFTER Filed March 26, 1962 I34 5 Sheets-Sheet 2 FIG. 8

INVENTORS FRANCIS J. LGRUSSA BY E NEST J. WILKINSON 5. 74 ATTORNEY June28, 1966 F. J. LA RUSSA ETAL 3,258,721

MICROWAVE PHASE SHIFTER Filed March 26, 1962 5 Sheets-$heet 5 3 SHORTPOSITION IL (INCHES) D v 0 l l l J 0 0.5 |.5 2 2.5 .D -m

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SHORT POSITION 1L (INCHES) INVENTOR. FIG 7 FRANCIS J. LclRUSSA BY ER ESTJ. WILKINSON ATTORNEY United States Patent "ice 3,258,721 MIQROWAVEPHASE SHTFTER Francis .1. La Russa, South Boston, and Ernest J.Wilkinson, Westwood, Mass., assignors to Sylvania Electric Productsllnc., a corporation of Delaware Filed Mar. 26, 1962, Ser. No. 182,343 8Claims. (Cl. 333-11) This invention relates generally to microwave phaseshifters and is more particularly concerned with phase shifters whichare controlled by varying the amplitude of an electrical signal.

There is a requirement in many electronic systems for a pair of equalamplitude signals whose relative phase can be continuously varied. Aparticular application having this requirement is a phased antenna arrayin which the relative phase of adjacent elements in the array must bevaried in order to scan the beam. Heretofore, duplicate phase shiftershave been required to produce a dual output with relative phase shift.Although duplicate phase shifters are suitable for some purposes, theyhave several disadvantages which limit their applicability, such as aneed for careful balance between the two phase shifters to insure thatthe outputs are of equal amplitude. Moreover, the size and weight ofduplicate phase shifters limits the applications in which they can beused.

With an appreciation of the foregoing limitations of the prior art,applicants have as a primary object of the present invention to provideapparatus for producing a pair of equal amplitude output signals therelative phase of which can be varied.

Another object of the invention is to provide apparatus in which therelative phase of a pair of output signals is varied in response to therelative amplitude of a pair of signals.

Another object of the present invention is to provide an amplitudecontrolled variable phase shifter in which the total power delivered tothe device remains constant.

A further object of the invention is to provide apparatus in which therelative phase of the output signals is varied with a single control.

Briefly, the invention resides in the novel combination of a powerdivider and a hybrid junction, the power divider providing a pair ofconstant phased voltages of variable amplitude which are applied to theinput terminals of the hybrid junction. Energization of the hybrid bythe constant phased voltages from the power divider causes a pair ofequal amplitude voltages at the output terminals of the hybrid whoserelative phase is varied in direct relation to the relative amplitude ofthe input signals, which, in turn, are determined by the setting of thepower divider.

The power divider may be constructed of either coaxial line, waveguide,stripline or a combination of these types, all of which are well knownin the art. The hybrid may also be any one of several well-known types,for example, coaxial line, stripline, waveguide or lumped parameter. Theonly limitation on the power divider is that its total output power mustbe constant in order for constant amplitude voltages to appear at theoutput terminals of the hybrid. That is, it is necessary to use a powerdivider which does not absorb energy in the process of dividing thepower between the two outputs.

The foregoing and other objects, features and advantages of theinvention, and a better understanding of its construction and operation,will become apparent from the following detailed description taken inconjunction with the accompanying drawings, wherein:

FIG. 1 is a pictorial view, partly diagrammatic, of one embodiment ofthe present invention;

FIGS. 2 and 3 are schematic diagrams of a hybrid junction and a powerdivider, respectively, useful in ex- 3,258,721 Patented June 28, 1966plaining the theory of operation of the present invention;

FIG. 4 is a pictorial view of another embodiment of the presentinvention;

FIG. 5 is a graph of the amplitude characteristic of a coaxial linepower divider of the type shown in FIG. 4;

FIG. 6 is a graph of the phase characteristic of a coaxial line powerdivider of the type shown in FIG. 4;

FIG. 7 is a graph of relative phase of the output signals from thehybrid junction versus the position of the short of the power dividerfor the embodiment shown in FIG. 4;

FIG. 8 is a partially cut-away pictorial view of another embodiment ofthe invention.

A waveguide version of the present invention, which is by way ofillustration only, is shown in FIG. 1 consisting of a hybrid junction10, commonly known in the art as a magic T, which is connected bywaveguides 12 and 14 here indicated diagrammatically, to a power divider16. The hybrid junction is well known in the microwave art and isdescribed, for example, in United States Patent 2,593,120, issued April15, 1952 to R. H. Dicke. It is well known that a voltage applied to thesum port 18 of a hybrid will produce equal amplitude in-phase voltagesat output ports 20 and 22, and a voltage applied to the difference port24 will produce equal amplitude voltages of opposite phase at ports 20and 22. An interesting property of a hybrid not generally recognized,however, is that the simultaneous application of quadrature phasedvoltages to ports 18 and 24 will produce equal amplitude output voltagesat ports 20 and 22 whose relative phase is dependent upon the relativeamplitude of the input voltages.

The power divider 16 is equally well known, being described, forexample, in United States Patent 2,605,356, issued July 29, 1952 to G.L. Ragan. While it is known that the position of the short circuits instubs 32 and 34 determines the relative amplitude of the output signalsfrom ports 28 and 30, it is not commonly known that the output signalsfrom ports 28 and 30 maintain a constant relative phase shift ofindependent of their relative amplitude. While the phase shift of theindividual signals varies with the amplitude, the difference in phasebetween the two signals remains constant at 90. The foregoing propertiesof the hybrid and power divider, together with their operation incombination will be more fully appreciated by considering the followingmathematical development.

Referring now to the schematic diagram of the hybrid in FIG. 2, it isknown that a voltage V applied to sum port 18 will produce outputvoltages at ports 20 and 22 which can be expressed as If a voltage V,which is in phase quadrature with V is applied to difference port 24,the output voltage at port 20 will be V '=j.7o7V, (2

and the output voltage at port 22 will be V '=j.707V (3) Now, ifvoltages V and V, are applied simultaneously to ports 18 and 24,respectively, the output voltages V at port 20 and V at port 22, will bethe sum of the input voltages, namely,

and

It is seen, therefore, that the magnitudes of the output voltages atports 20 and 2 2 are equal, and depend only on the sum of the squares ofthe input voltages, or stated another way, the magnitude of the outputvoltages is dependent only on the total power into the hybrid. As longas the total input power remains constant, the amplitude level at theoutput ports will remain constant.

The phase of the output voltages at ports 20 and 22, however, isdependent on the relative amplitude of the input voltages, as shown byEquations 4 and 5. Dividing Equations 4 and 5, we obtain which is therelative phase angle of the output signals at ports 20 and 22 and isseen to be directly related to the input voltages.

Referring now to FIG. 3 which is a schematic diagram of a power dividerof the type described by Ragan, it will be shown that the power divideris capable of supplying to the hybrid a pair of voltages of variablemagnitude but whose relative phase remains constant at 90.

It is well known, as exemplified by page 556 of the fourth edition ofthe ITT Handbook, Reference Data for Radio Engineers, that the voltagesat terminals 26, 28 and 30 of the power divider are related by V V J (8)where Yb w cot a 1 Q-ld-j tan A where l is the distance to the shortcircuit on stub 34, as shown. From Equations 7 and 8, it follows thatnan and from Equations 9, 10 and 11 Y /Y can be expressed as whichclearly indicates that the relative phase angle of the signals appearingat output ports 28 and 30 remains constant at 90.

The input admittance Y, at port 26 can be written as 21rl 1-1 cot 1+tanwhich indicates that the input admittance Y,, is always matched to thecharacteristic admittance of the line, and

is independent of stub length l.

When the power divider output ports 28 and 30 are connected to the inputports 18 and 24 of the hybrid, V /V is the same as V /V and Equation 6can be written XL Vs'r 6 (1 from which it is apparent that the relativephase of the signal at the hybrid output ports 20 and 22 varies linearlywith the length l of the short circuited stubs 32 and 34 of the powerdivider. Thus it is evident that the relative phase angle of the signalsat ports 20 and 22 of the hybrid can be varied by a single controlarranged to alter the length l of stubs 32 and 34.

FIG. 4 illustrates another embodiment of the invention wherein a coaxialline power divider 60 of the type shown in the Ragan patent is connectedby equal length coaxial cables 62 and 64 to a hybrid 66 of the typeknown in the art as a rat race. A voltage applied to the input port 76of the divider is divided between output ports 78 and 80 in accordancewith the position of the short circuits in stubs 82 and 84, as adjustedby ganged arm 86, and applied through the coaxial cables to input ports88 and 94 of the hybrid. As has previously been discussed, the variableamplitude voltages applied to'the hybrid input port-s are in phasequadrature thereby causing equal amplitude output voltages to appear atports 92 and 90 whose relative phase is directly related to the ratio ofthe voltages at ports 78 and 80 of the power divider.

FIGS. 5 and 6, respectively, show the measured amplitude and phasecharacteristics of a power divider of type shown in FIG. 4. A 2400 me.signal was applied to terminal 76 of the power divider and the amplitudeand phase of the output signals at terminals 78 and 80 were measuredusing standard slotted line techniques. FIG. 5 shows that the ratio V Vvaries according to the function tan T as has been expressed by Equation12, while FIG. 6 shows the phase angle between the output signals issubstantially constant over a relatively large range of short positions.

The slight departure of the amplitude characteristic of FIG. 5 from atrue tangent curve, and the gradual, rather than instantaneous change inphase at the quarter wave points of the characteristic of FIG. 6 areprobably due to leakage past the less than ideal short circuits betweenthe conductors of the power divider, and the interaction between theoutput voltages in the slotted line measuring equipment.

The linear phase variation with stub position I, predicted by Equation14, is depicted by the dotted line curve in FIG. 7. The solid line curveindicates the values obtained when a 2400 me. signal was applied toterminal 76 and the relative phase angle of the output signals at ports92 and 94 measured as the stub position I was varied. The slightnon-linearity of the measured curve is due to the causes which havealready been noted.

FIG. 8 illustrates a further embodiment of the invention wherein thepower divider and hybrid are combined in a compact integral unit. Thehybrid, again of the stripline rat race type, comprises a ring-shapedstrip conductor sandwiched between dielectric plates 102 and 104 withmetal plates 106 and 108 forming the ground planes. The output terminals110 and 112 extend radially outward and are circumferentially spaced byan integral number of half wavelengths at the frequency of operation. Inthe disclosed configuration, the hybrid is not provided with inputterminals in the usual sense, the input signals instead being coupleddirectly to the ring at points 114 and 116 respectively located the sameintegral number of quarter wavelengths counterclockwise from outputcon-.

nections 110 and 112, with point -114 being midway between terminals 110and 112.

The power divider is partially contained in the stripline structure, theinput terminal thereof being coupled to an L-shaped conductor havingarms 120a and 12% which extend radially outward to points 114 and 116 atwhich they are joined with ring-shaped conductor 100. A pair of coaxialline stubs 122 and 124 extend perpendicularly upward from the plane ofthe stri-pline structure, with their inner conductors joined to ring 100and points 114 and 116 and their outer conductors electrically connectedto ground plane 106. The stubs are provided with movable shorting disc-s126 and 128 which are ganged for movement in unison by a pair of rods130 and 132 cross-connected by a suitable handle 134. The rods may beformed of a dielectric material, as shown, in the interests of reducingweight and wear, or they may be formed of conducting material, ifdesired. It will be seen that the output terminals of the power dividerare also at points 114 and 116, and thus coincident with the inputterminals of the hybrid. A signal applied to input terminal 118 producesequal amplitude output signals at terminals 110 and 112 the relativephase of which may be varied by adjustment of the position of theshorting discs 126 and 128.

While there has been described what are now believed to be preferredembodiments of the invention, many modifications and changes can be madewithout departing from the spirit and scope of the invention. Forexample, a variety of power dividers and hybrid junctions can be used,such as waveguide, coaxial line, stripline, lumped circuit or acombination thereof; Also, the two devices can be integrated in manyway-s which will occur to those skilled in the art. Further, a hybrid ofthe type' described requiring input signals with a constant 90 phaseshift is illustrative only, as other types of hybrids having differentinput requirements can be used to produce the desired re sult. Forexample, a branched line coupler, of the type described on page 866 ofvolume II of the Massachusetts Institute of Technology RadiationLaboratory Series, can be used if constant in-phase signals, which arerequired to energize this hybrid, are provided. The in-phase signalscould be provided by adding a quarter wavelength transmission line toone of the arms of the power divider. Accordingly, it is not intended tolimit the scope of the present invention by what has been particularlydescribed except as indicated in the appended claims.

What is claimed is:

1. Microwave phase shifting apparatus comprising the combination of apower divider having two stubs with slidable short circuits thereon forvarying the relative power'between a pair of outputs while maintaining aconstant relative quadrature phase, and a hybrid junction having twoinput terminals and two output terminals, said input terminals connectedto said power divider outputs whereby a pair of equal amplitude signalsare produced at the output terminals of said hybrid junction whoserelative phase is dependent on the position of said slidable shortcircuits.

2. Microwave apparatus comprising ring-shaped transmission line havingtwo output terminals connected thereto and an integral number of halfwavelengths apart, two impedance changing means connected to said ringshaped line, said impedance changing means being separated by anintegral number of half wavelengths with one of them located midwaybetween said output terminals, and an input terminal connected to saidring-shaped line to points of connection common with said impedancechanging means, said input terminal being connected to said ringshapedline by transmission lines each an odd number of quarter wavelengthslong.

3. Microwave apparatus comprising a ring-shaped conductor having twooutput terminals connected thereto an integral number of halfwavelengths apart, two coaxial lines connected to said ring conductor,said coaxial lines being separated by an integral number of halfwavelengths with one of them located midway between said outputterminals, a slidable short circuiting contact on each of said coaxiallines, said contacts arranged an integral number of quarter wavelengthsapart, means for moving said contacts in unison such that the quarterwavelength spacing between said contacts is maintained, and an inputterminal connected by quarter wavelength conductor to said ring-shapedconductor at points of connection common with said coaxial lines.

4. Microwave apparatus comprising a ring-shaped conductor having twooutput terminals connected thereto an integral number of halfwavelengths apart, two shortcircuited stubs connected to saidring-shaped conductor, said stubs being spaced apart an integral numberof half wavelengths with one of them located midway between said outputterminals, means for altering the length of said stubs while maintaininga quarter wavelength spacing between said short circuits, and an inputterminal connected by quarter wavelength conductors to said ringshapedconductor at the same points of connection as said stubs.

5. Microwave phase shifting apparatus comprising a ring-shaped conductorhaving four terminals connected thereto at points spaced from each otherby an integral number of quarter wavelengths, two coaxial lines eachhaving a slidable short circuit thereon, said coaxial lines beingconnected to an alternate two of said terminals, an input terminal alsoconnected to said alternate two terminals by quarter wavelengthconductors, and means for slidably adjusting said short circuits whilemaintaining a quarter wavelength spacing between said short circuits,whereby a signal applied to said input terminal will cause equalamplitude signals to appear at the other two of said terminals whosephase is variable in response to adjustment of the positions of saidslidable short circuits.

6. Microwave phase shifting apparatus comprising a ring-shaped conductorsupported between and electrically insulated from two parallelconducting plates, two output terminals connected to said ring conductorat points separated by an integral number of half wavelengths, twocoaxial lines having inner and outer conductors, the inner conductors ofsaid lines being connected to said ring conductor and the outerconductors thereof being connected to one of said conducting plates, thepoints of said coaxial lines to said ring-shaped conductor being spacedapart an integral number of half wavelengths with one of them locatedmidway between said output terminals, a slidable short-circuitingcontact on each said coaxial lines spaced from each other an odd numberof quarter wavelengths, means for moving said contacts in unison whilemaintaining said quarter wavelength spacing, and an input terminalconnected to said coaxial lines by quarter wavelength conductorssupported in the plane of said ring-shaped conductor, wherein a changein the position of said slidable contacts will cause a change in therelative phase between the signals appearing at said output terminals.

7. A microwave phase shifter operative to produce a pair of signalshaving equal amplitude and variable rela tive phase said phase shiftercomprising, means for producing a pair signals of variable relativeamplitude and constant relative quadrature phase, and hybrid meansdirectly connected to said first mentioned means for producing inresponse to said pair of signals a pair of output signals of equalamplitude and whose relative phase is dependent on the relativeamplitude of said pair of quadrature phased signals.

8. Microwave phase shifting apparatus comprising the combination of apower divider having an input terminal, two output terminals, and meansfor varying in response to a signal applied to said input terminal therelative amplitude of signals appearing at said output terminals whilemaintaining the relative phase between said signals in quadrature, and ahybrid junction having two input 7 terminals and two output terminals,said input terminals connected to said power divider output terminalswhereby a pair of equal amplitude signals are produced at the outputterminals of said hybrid junction whose relative phase is dependent onthe relative amplitude of the quadrature phased signals from said powerdivider.

References Cited by the Examiner UNITED STATES PATENTS Fox 33311Tillotson 333--9 Grieg et a1 33311 Pan 333-9 Wheeler 333--7 Petrich333-11 Marcatili 3339 Budenbom 3339 10 HERMAN KARL SAALBACH, PrimaryExaminer.

C. BARAFF, Assistant Examiner.

8. MICROWAVE PHASE SHIFTING APPARATUS COMPRISING THE COMBINATION OF APOWER DIVIDER HAVING AN INPUT TERMINAL, TWO OUTPUT TERMINALS, AND MEANSFOR VARYIONG IN RESPONSE TO A SIGNAL APPLIED TO SAID INPUT TERMINAL THERELATIVE AMPLITUDE OF SIGNALS APPEARING AT SAID OUTPUT TERMINALS WHILEMAINTAINING THE RELATIVE PHASE BETWEEN SAID SIGNALS IN QUADRATURE, AND AHYBRID JUNCTION HAVING TWO INPUT TERMINALS AND TWO OUTPUT TERMINALS,SAID INPUT TERMINALS CONNECTED TO SAID POWER DIVIDER OUTPUT TERMINALSWHEREBY A PAIR OF EQUAL AMPLITIDE SIGNALS ARE PRODUCED AT THE OUTPUTTERMINALS OF SAID HYBRID JUNCTION WHOSE RELATIVE PHASE IS DEPENDENT ONTHE RELATIVE AMPLITUDE OF THE QUADRATURE PHASED SIGNALS FROM SAID POWERDIVIDER.